Digital to analog (D/A) converters are well known and are used to convert digital signals representing information into analog signals representing the same information. In instrumentation devices, D/A converters are used to convert received digital signals into analog signals that are applied to the internal circuitry of the instrument to effect a system or device function represented by the received digital signal. A single instrument may use a plurality of D/A converters to control a corresponding plurality of device functions. Although D/A converters are currently available in many different configurations and types, modern instrumentation technology imposes a set of constraints and requirements that is not met by the currently available D/A converters. As mentioned, a single instrument may require the use of a plurality of D/A converters. Since space is often at a premium in instruments, the required plurality of D/A converters must occupy a minimum of space. This leads to the requirement that the plurality of required D/A converters should be on a single chip rather than comprise a plurality of discrete devices.
The plurality of D/A converters in an instrument need not be necessarily of the same type since the different converters will control different device functions. Some of these functions are complex. Others are relatively simple. A first D/A converter may control a complex function by generating an analog output signal having a large number of discrete steps. This may require the use of a 16 bit D/A converter in order to provide 65536 different levels in the output signal. Another converter may need only generate an output signal having 256 different amplitudes. In this case, an 8 bit converter may be used. Still another converter may perform a relatively simple function such as a "yes or no" or an "on/off" function. In this case, a one bit converter would be adequate. The need for converters that operate from data words of different bit sizes has heretofore required the use of different A/D converter devices. This increases the cost and complexity of the instrument design.
Current day state-of-the-art instrumentation requires extremely close tolerances on output voltages and other specifications of the signals operating the instrument. This requires that the D/A converters provide output signals that have a correspondingly close tolerance on the amplitude of the output signals as well as the signal duration.
Although many different types of D/A converters are currently available, none is available that meets all of the above characterized requirements. D/A converters are primarily available as discrete devices and not on chips containing a plurality of converters. There are no D/A converters capable of operating with input signals containing different numbers of data bits such as 1 bit, 4 bits, 8 bits, 16 bits, etc.
It may be seen in view of the above that although D/A converters are well known and extensively used, it is a problem to use the currently available converters in state of the art instrumentation in a manner that meets all of the above requirements.